Topoisomerase I promotes the relaxation of DNA superhelical tension by introducing a transient single-stranded break in duplex DNA and are vital for the processes of replication, transcription, and recombination [2]. This family may be more than one structural domain.

1: The mechanisms of DNA topoisomerases. Roca J; Trends Biochem Sci 1995;20:156-160. PMID:7770916

2: Crystal structures of human topoisomerase I in covalent and noncovalent complexes with DNA. Redinbo MR, Stewart L, Kuhn P, Champoux JJ, Hol WG; Science 1998;279:1504-1513. PMID:9488644